In the usual practice for manufacturing dichloroacetyl chloride (DCAC) in the liquid phase, trichloroethylene (TCE) is treated with oxygen and/or air in the presence of a catalytic amount of free chlorine and a chlorine activating source such as short wavelength light, usually ultraviolet light with vigorous agitation under pressure. The photo-oxidation of trichloroethylene provides approximately a 50:50 mixture of dichloroacetyl chloride and trichloroethylene oxide (TCEO).
After this reaction is essentially complete, the mixture of dichloroacetyl chloride and trichloroethylene oxide is subjected to an exothermic catalytic rearrangement of the trichloroethylene oxide to dichloroacetyl chloride. This is brought about by adding a secondary or tertiary amine catalyst to the reaction mixture while cooling the same. A secondary or tertiary amine has been described as dimethyl amine, diethyle amine, dibutyl amine, trimethyl amine, triethyl amine, tributyl amine, N-methylaniline, N,N-dimethylaniline, pyridine, piperdine, picolines, quinolines and mixtures of these amines. The prior art described processes indicates that essentially quantitive yields of rearrangement from trichloroethylene oxide to dichloroacetyl chloride are obtained. A more complete description of prior art processes may be found in U.S. Pat. No. 3,630,867.
It has been found in practice, however, that the manufacture of dichloroacetyl chloride by the above-described process has serious drawbacks. First, since the rearrangement reaction of trichloroethylene oxide to dichloroacetyl chloride is both rapid and exothermic, a serious problem of control of the rearrangement reaction results upon addition of the secondary or tertiary amines at or near the end of the oxidation of trichloroethylene. And second, upon addition of the secondary or tertiary amines to the reaction during the course of the reaction, to effect the rearrangement of the trichloroethylene oxide to dichloroacetyl chloride as it is formed, colored by-product chemical species are formed, which as the rearrangement reaction progresses effect the color of thereaction mass, changing it from clear to a light amber to dark brown or purple. The specific color will, of course, depend upon the amount of secondary or tertiary amines being employed as catalyst. As the rearrangement reaction of trichloroethylene oxide to dichloroacetyl chloride proceeds, the increase in the intensity of the color bodies tends to inhibit the passage of ultraviolet light rays through the reaction mass resulting in a substantial inhibition of the reaction rate resulting in slower overall reaction rates which are commercially unattractive. Upon completion of the reaction the color bodies must be removed prior to use of the dichloroacetyl chloride by oxidation of the colored species. The continued oxidative contact of the reaction mass results in further degradation of the dichloroacetyl chloride present in the reaction mass to such undesirable by-products as phosgene.